In recent years, electrophoretic displays have been drawing attention as a reflective display device having a low power consumption and a good visibility. Patent Document No. 1 and Non-Patent Document No. 1 each disclose an electrophoretic display capable of producing color display as well as black and white display.
FIG. 34 shows an electrophoretic display 700 disclosed in Patent Document No. 1. FIG. 34 is a cross-sectional view schematically showing the electrophoretic display 700.
As shown in FIG. 34, the electrophoretic display 700 includes a TFT substrate 710, a counter substrate 720 that faces the TFT substrate 710, and an electrophoretic layer 730 provided between the TFT substrate 710 and the counter substrate 720.
The TFT substrate 710 includes a plurality of TFTs 711 arranged in a matrix pattern, and pixel electrodes 712 electrically connected respectively to the TFTs 711. The plurality of TFTs 711 and the pixel electrodes 712 are supported by a glass substrate 710a. 
The counter substrate 720 includes a counter electrode 722 provided so as to face the pixel electrode 712. The counter electrode 722 is supported by a glass substrate 720a. 
The electrophoretic layer 730 includes a dispersion medium 731, and cyan-colored, magenta-colored and yellow-colored electrophoretic particles (hereinafter referred to respectively as “cyan particles”, “magenta particles” and “yellow particles”) 732C, 732M and 732Y dispersed in the dispersion medium 731. The electrophoretic layer 730 further includes white-colored supports 733 for holding cyan particles 732C, magenta particles 732M and the yellow particles 732Y.
The cyan particles 732C, the magenta particles 732M and the yellow particles 732Y are charged with the same polarity and have different threshold voltages from each other. The supports 733 are charged with a different polarity from the cyan particles 732C, the magenta particles 732M and the yellow particles 732Y.
With the electrophoretic display 700, the cyan particles 732C, the magenta particles 732M and the yellow particles 732Y are moved in the thickness direction (cell thickness direction) of the electrophoretic layer 730 by using a vertical electric field that is generated in the electrophoretic layer 730 when a voltage is applied between the pixel electrode 712 and the counter electrode 722. Patent Document No. 1 proposes an approach in which a voltage is applied through the electrophoretic layer 730 while properly varying the applied voltage level over a plurality of subframes, thereby individually controlling the density distribution of the various particles in the cell thickness direction, thus realizing multi-gray level display.
FIG. 35 shows the electrophoretic display 800 proposed in Non-Patent Document No. 1. FIG. 35 is a cross-sectional view schematically showing an area corresponding to one pixel of the electrophoretic display 800.
As shown in FIG. 35, the electrophoretic display 800 includes a lower glass substrate 801, an upper glass substrate 802, and oil 831 sealed therebetween. First particles 832P and second particles 832N are dispersed in the oil 831. The first particles 832P are positively charged, and the second particles 832N are negatively charged. The first particles 832P and the second particles 832N are in colors (e.g., magenta and green) that are complementary to each other.
A first migration electrode 811, a second migration electrode 812 and a gating electrode 813 are provided on the lower glass substrate 801. The first migration electrode 811 is placed at one end of the pixel, and the second migration electrode 812 is placed at the other end of the pixel. The gating electrode 813 is placed between the first migration electrode 811 and the second migration electrode 812. Note however that the gating electrode 813 is located in the vicinity of the first migration electrode 811. That is, the interval between the first migration electrode 811 and the gating electrode 813 is significantly smaller than the interval between the gating electrode 813 and the second migration electrode 812. When there is a potential difference between adjacent ones of the first migration electrode 811, the second migration electrode 812 and the gating electrode 813, a transverse electric field is generated between the electrodes, and the first particles 832P and/or the second particles 832N migrate in accordance with the transverse electric field. The region between the gating electrode 813 and the second migration electrode 812 is the region (opening region) that contributes to display. A back reflector 850 is placed on the back side of the lower glass substrate 801.
Referring to FIGS. 36(a), 36(b) and 36(c), display principles of the electrophoretic display 800 will now be described.
The electrophoretic display 800 is switched between four states shown in FIG. 35, FIGS. 36(a), 36(b) and 36(c) by controlling the relative levels of the potentials applied to the first migration electrode 811, the second migration electrode 812 and the gating electrode 813.
In the state shown in FIG. 35, the first particles 832P and the second particles 832N are both positioned between the gating electrode 813 and the second migration electrode 812. Therefore, this state produces display based on subtractive color mixing between the color of the first particles 832P and the color of the second particles 832N, i.e., black display.
In the state shown in FIG. 36(a), neither one of the first particles 832P and the second particles 832N is positioned between the gating electrode 813 and the second migration electrode 812. Therefore, this state produces display based on light that is reflected by the back reflector 850, i.e., white display.
In the state shown in FIG. 36(b), only the second particles 832N, of the first particles 832P and the second particles 832N, are positioned between the gating electrode 813 and the second migration electrode 812. Therefore, this state produces display of the color of the second particles 832N (e.g., green).
In the state shown in FIG. 36(c), only the first particles 832P, of the first particles 832P and the second particles 832N, are positioned between the gating electrode 813 and the second migration electrode 812. Therefore, this state produces display of the color of the first particles 832P (e.g., magenta).
Thus, the electrophoretic display 800 of Non-Patent Document No. 1 realizes color display by using the three electrodes 811, 812 and 813 that generate a transverse electric field, and two types of particles 832P and 832N that are charged with different polarities from each other.